Study On Constitutive Relation Of Recycled Aggregate Concrete Damaged By Freeze-thaw Under Monotic And Cyclic Loading

The insufficient durability of engineering structure, such as roads, bridges and cooling towers, which is located in the cold region, is widespread because of freeze-thaw damage. As an important method to recycle waste concrete, research on recycled aggregate concrete has drawn more and more attention. The purpose of this paper is to provide theoretical support for recycled aggregate concrete used in the cold region, through measuring and studying the complete stress-strain curve of recycled aggregate concrete damaged by freeze-thaw under monotonic and cyclic loading. Specific studies are as follows:(1) With different replacement rates of the recycled coarse aggregate and different numbers of freeze-thaw cycles, 72 standard prismatic specimens were subjected to rapid freeze-thaw cycle test, the highest times of rapid freeze-thaw cycle test was 300. Measured the quality and revelative dynamic elastic modulus of each group, and then established the relationship between quality loss rate, relative dynamic elastic modulus and numbers of freeze-thaw cycles.(2) 36 recycled aggregate concrete specimens damaged by freeze-thaw under monotonic loading were accomplished to observe each group’s failure modes and measured the complete stress-strain curve of each group. Under different recycled aggregate displacement ratio, the relation between peak stress, peak strain, ultimate strain, elastic modulus, lateral deformation coefficient an d numbers of freezing-thawing cycleswas established. Fitted the rising step of stress strain relation curve with a third order polynomial, fitted the descending portion of the curve with a rational fraction equality, and established uniaxial compression constitutive model of recycled aggregate concrete damaged by freeze-thaw.(3) Comparing with monotonic loading experiments, 36 recycled aggregate concrete specimens damaged by freeze-thaw under cyclic loading were accomplished to observe failure modes of each group and measure d the complete stress-strain curve of each group. Based on the test results of 36 concrete samples, differences and similarities between envelopes of complete stress-strain curve under cyclic loading and stress-strain curve under monotonic loading were analysed. Established equations of unloading curves and reloading curves, equations between unloading curve parameters, reloading curve parameters and numbers of freezing-thawing cycles were established respectively. Established uniaxial compression constitutive model of recycled aggregate concrete damaged by freeze-thaw under cyclic loading.